Objective Morality: Realism, Anti-Realism, and Evolutionary Debunking

SUMMARY

The debate over objective morality asks whether moral judgments track mind-independent moral facts or are instead expressions of preferences, conventions, or evolutionary contrivances. The question has gained urgency in contemporary philosophy through evolutionary debunking arguments — most prominently Sharon Street's "Darwinian Dilemma" (2006) — which claim that the evolutionary origins of moral intuitions render the realist position untenable. Within the project framework, the question is part of Maslik 3 (Human): if moral intuitions appear to track objective truths in ways that resist evolutionary debunking, this constitutes a probability shift toward the insufficiency of materialist explanation for the full human phenomenon.

The Realist / Anti-Realist Map

The metaethical landscape can be mapped (with some loss of nuance) along two axes. The first axis: are there moral facts at all? The second axis: if there are, what is their status?

Moral realism holds that there are mind-independent moral facts. Different realists differ on the nature of these facts:

Naturalist realism holds that moral facts are reducible to or identical with natural facts (well-being, survival, social functioning). Cornell realism (Boyd, Sturgeon, Brink) and contemporary neo-Aristotelian virtue ethics (Foot, Hursthouse) exemplify this position.
Non-naturalist realism holds that moral facts are real but irreducible to natural facts. G. E. Moore's Principia Ethica (1903) is the foundational text; contemporary defenders include David Enoch (Taking Morality Seriously, 2011), Russ Shafer-Landau (Moral Realism: A Defence, 2003), and Derek Parfit (On What Matters, 2011).
Theistic realism holds that moral facts depend constitutively on God — divine command theory in various forms, or natural law theory in its theistic versions.

Moral anti-realism denies mind-independent moral facts. Variants:

Error theory (J. L. Mackie, Ethics: Inventing Right and Wrong, 1977) holds that moral claims aim to refer to objective facts but systematically fail; all positive moral claims are false in the way "the present King of France is bald" is false.
Expressivism / non-cognitivism (A. J. Ayer, Charles Stevenson, Simon Blackburn, Allan Gibbard) holds that moral claims are not assertions but expressions of attitudes; they do not aim at truth in the realist sense.
Constructivism (Sharon Street, Christine Korsgaard) holds that moral facts are real but constructed through the standpoint of rational agents.

The classical Islamic tradition presents its own distinctive map: the Muʿtazila tended toward objective moral realism (good and evil are knowable by reason independently of revelation), while the Ashʿariyya tended toward divine command theory (good is what God commands, and what makes acts good is God's command rather than any independent property). The classical kalām debate parallels the modern realism/anti-realism debate in interesting ways.

The Evolutionary Debunking Challenge

The most influential contemporary argument against moral realism comes from evolutionary considerations. Sharon Street's "A Darwinian Dilemma for Realist Theories of Value" (Philosophical Studies, 2006) presents the argument with particular force.

Street's argument runs:

Evolutionary forces have substantially shaped the content of human moral intuitions.
The realist must take a position on the relation between these evolutionary forces and the alleged moral truths.
The realist faces a dilemma: either accept that there is no relation between the evolutionary forces and moral truth — in which case the reliability of our moral judgments becomes mysterious — or claim that there is a relation, which requires explaining how evolution managed to track moral truths it had no selective reason to track.
Both horns are unacceptable.
Therefore moral realism is untenable.

Richard Joyce develops a parallel argument in The Evolution of Morality (2006), with a focus on the evolutionary origins of moral judgment as a kind of debunking story for the authority of moral intuitions.

The argument is taken seriously even by those who reject it. Its force depends on the empirical claim about evolutionary influence (widely granted), the philosophical claim about what realism requires (more contested), and the inferential claim that the realist cannot meet both demands (the principal point of disagreement).

The Realist Response

Several realist responses to evolutionary debunking have been developed:

David Enoch's third-factor response (Taking Morality Seriously, 2011) argues that there can be a third factor that explains both the moral truths and our tendency to track them — most plausibly, a teleological structure of natural selection that, given the existence of moral truths, would tend to produce creatures with reliable moral intuitions. Critics including Sharon Street herself have argued that this response covertly presupposes what it must establish.

Russ Shafer-Landau's appeal to moral knowledge (Moral Realism: A Defence, 2003; later papers) argues that the existence of moral knowledge is itself good evidence that we have moral knowledge — that the debunking argument, taken to its conclusion, undermines its own ability to make the case it tries to make.

The "evolution as a coincidence detector" response argues that even if evolution does not directly track moral truth, selection pressures favored agents able to detect features (social cooperation, harm avoidance, fairness) that are in fact morally significant. The reliability of moral intuition is then an indirect consequence of selection for tracking features that happen to overlap with moral facts.

The transcendental response argues that moral realism is presupposed by the practical engagements of any rational agent — that to deliberate seriously about what to do is already to operate within a realist framework that one cannot coherently reject.

Theistic realist responses argue that on a theistic worldview, the alignment between evolutionary processes and moral truths is unsurprising: God could have designed the evolutionary process to produce moral agents capable of tracking the moral order. This response is sometimes characterized as moving the question rather than settling it; it is also, to put the point sharply, the one most relevant to the framework's interest in Maslik 3 as contributing to the cumulative case.

The Empirical Layer

An important development in recent decades has been the experimental investigation of moral intuitions. Joshua Greene's work on the neural basis of utilitarian vs. deontological judgments (Moral Tribes, 2013) attempts to debunk certain moral intuitions by tracing them to evolutionarily ancient emotional responses. Other empirical work — Jonathan Haidt's moral foundations theory, Frans de Waal's work on primate morality, cross-cultural moral psychology — supplies the empirical ground that debunking arguments rely on.

The relationship between the empirical work and the philosophical conclusion is itself contested. Some philosophers (Greene himself, Peter Singer) take the empirical work to support debunking. Others argue that explaining the psychological mechanisms by which we form moral judgments is logically independent of evaluating the authority of those judgments — the genetic fallacy concern again.

What This Question Establishes for Maslik 3

Within the framework, the objective morality debate contributes to Maslik 3 in the following way:

If the realist position is genuinely tenable in the face of evolutionary debunking, this constitutes a probability shift toward the view that human moral cognition tracks something beyond what biological evolution alone would predict.
If theistic realism provides the most natural framework for explaining how moral knowledge is possible, this constitutes a further probability shift toward theism specifically.
The framework does not claim either of these conclusions is established with yaqīn; the debate is genuinely contested and reasonable persons disagree.

Importantly, the moral question is one of the strongest sites for the Maslik 3 argument because:

The realist intuition is widely shared, even among committed naturalists. The conviction that torturing children for fun is really wrong, not just socially disapproved, is a starting point that survives extensive philosophical pressure.
The debunking arguments, taken to their conclusion, produce conclusions that many find practically unlivable (genuine moral nihilism vs. the felt authority of moral demands).
The relationship between moral realism and theism is direct in a way that the relationship between, say, the hard problem of consciousness and theism is not. Moral realism can be defended on non-theistic grounds, but theistic realism provides a particularly natural explanatory framework.

KEY DISTINCTIONS

• Moral realism vs. anti-realism: Whether there are mind-independent moral facts • Naturalist vs. non-naturalist realism: Whether moral facts reduce to natural facts • Cognitivism vs. non-cognitivism: Whether moral claims aim at truth or express attitudes • Error theory vs. expressivism: Two principal versions of anti-realism • Debunking vs. genetic-fallacy concerns: Explaining the origin of moral beliefs vs. impugning their authority • Muʿtazilī objective good vs. Ashʿarī divine command: The classical Islamic version of the debate • Real vs. constructed objectivity: Street's constructivism aims to preserve the appearance of objectivity within an anti-realist framework

MAJOR PROPONENTS (of realism)

• G. E. Moore — Principia Ethica (1903); founding non-naturalist realism • David Enoch — Taking Morality Seriously (2011); robust realism • Russ Shafer-Landau — Moral Realism: A Defence (2003) • Derek Parfit — On What Matters (2011); convergent realism • Philippa Foot — Natural Goodness (2001); neo-Aristotelian naturalist realism • Rosalind Hursthouse — Virtue-theoretic realism • C. S. Lewis — Mere Christianity, The Abolition of Man; popular theistic articulation • Linda Zagzebski — Divine Motivation Theory (2004); theistic realism • The Muʿtazila — Classical Islamic objective moral realism (al-Naẓẓām, ʿAbd al-Jabbār)

MAJOR CRITICS (of realism)

• J. L. Mackie — Ethics: Inventing Right and Wrong (1977); error theory • A. J. Ayer — Language, Truth and Logic (1936); emotivism • Simon Blackburn — Spreading the Word (1984); quasi-realist expressivism • Allan Gibbard — Wise Choices, Apt Feelings (1990); norm-expressivism • Sharon Street — "A Darwinian Dilemma" (2006); constructivism + debunking • Richard Joyce — The Evolution of Morality (2006); evolutionary debunking • Joshua Greene — Moral Tribes (2013); neural debunking of deontological intuitions